Patent GB-1520841-A (GB)
Title: Method and apparatus for folding and welding the heat weldable edge of a cover sheet to a base sheet
IPC: B29C65/04
Filed: 1976-05-10
Abstract: 1520841 Folding edges of non-metallic sheet material TOMITA SANGYO KK 10 May 1976 19165/76 Heading B5K The heat weldable marginal edge 2<SP>1</SP>, Fig. 8, of a cover sheet 2, e.g. of vinylic resin or weldable non-woven fabric, is folded over the periphery of a base sheet 4, e.g. cardboard having both faces coated with vinylic resin, by die sections 31 drawn together from an expanded state by a rotatable element 35 on a die frame 3, and the edge 2<SP>1</SP> is bonded to the sheet 4 by heating welding elements on the frame 3. In the embodiment shown, a press apparatus 1, Fig. 2, comprises an air cylinder 11, a contact head 13 on a guide rod (12), Fig. 1 (not shown), a limit switch 14, a horizontal table 15, electrically insulating connecting rods 16, and a press table 17 on a platform 18. The die frame 3, e.g. of copper, is suspended by an assembly 5 and comprises four sections 31, Fig. 8, normally disposed in the positions of Fig. 6. Each section 31 has an integral sheet 32 slidable on the lower surface of the assembly 5 and has an arm 34 pivoted thereto and to a disc 35 rotatably mounted on the assembly 5. Heat insulating sheets 311 are rivetted to one or both sides of each section 31, Fig. 8. Each sheet 32 has two rhombic rims 32<SP>1</SP>, Fig. 6, provided with guide recesses 37 partly occupied by fixed members 33. A driving handle 36, Fig. 3, is provided on the upper surface of the assembly 5 and is fixed to the disc 35. To move the sections 31 from the positions of Fig. 6 to those of Fig. 5, an air motor 71, Fig. 2, is driven so that a roller 74, Fig. 3, on an L-shape lever (73), Fig. 1 (not shown), slides in a groove 38 in the handle 36 to swing the handle to rotate the disc 35 so that the sections 31 are drawn inwardly. On the upper surface of the assembly 5, Fig. 3, a copper electrode holder 51 is mounted and carries electrodes 91 of a high frequency generator. The table 15 is connected to earth 92. T-shape push bars 54, Figs. 3 and 8, carrying a panel 53, pass through sleeves 55 on the assembly 5, springs 56 acting between the bars 54 and the sleeves 55. In operation, the sheet 2 is placed over a recess on the table 17 and the sheet 4 is placed thereover. A start switch (19), Fig. 1 (not shown), is depressed so that the cylinder 11 lowers the assembly 5 to the position of Fig. 8 in which the switch 14 contacts the rod head 13 to actuate the motor 71 and to cause further lowering of the assembly 5 to expand the springs (56), Fig. 9 (not shown). Actuation of the motor 71 causes the sections 31 to be drawn inwardly so that the upwardly projecting edge 2<SP>1</SP> of the sheet 2 is folded down on to the upper surface of the sheet 4, Fig. 10 (not shown). A timer (not shown) supplies h.f. electric current to the electrodes 91 to heat the edge 2<SP>1</SP> to weld it to the sheet 4. After a predetermined time, the current is interrupted and the assembly 5 is raised and the sections return to their Fig. 6 position. During the welding, a temperature of, for example, 180 C. is applied to the portion of the edge 2 in direct contact with the lower face of the sections 31, 120 C. to the portion in contact with the interface between the sections 31 and the sheets 31<SP>1</SP> and 100 C. to the portion near the folding line of the edge 2<SP>1</SP> so that varying amounts of heat are applied across the width of the edge 2<SP>1</SP>. A thin insulating sheet may be provided directly on the lower end face of the frame 3.